1. Field of the Invention
The present invention relates to improvements in a shift control of an automatic transmission, and more particularly to a hydraulic control for friction elements during a shift.
2. Description of the Prior Art
A conventional automatic transmission system includes a plurality of friction elements which selectively change the connecting state for a shift. The change of the connecting state of the friction elements is carried out by controlling a hydraulic circuit included in the automatic transmission system. For example, the hydraulic pressure of one friction element (release element) is lowered to zero for setting the friction element at a released state, and the hydraulic pressure of another friction element (apply element) is raised to a predetermined value for setting the another friction element at an engaged state.
However, if the shift taking place in the above mentioned system is a foot-released upshift, after which a downshift is often carried out, it takes a predetermined time to engage the released friction element such that a downshift can take place immediately after the upshift. Accordingly, this may cause a discomfort shock during the downshift.